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Description
Currently few doubt that a common approach with a gas target for a negative ion beam neutralization in large NB-heating systems is not enough promising. Photon neutralization is considered as main alternative to gas target for injection efficiency enhancement. Significant power density of photons in steady state is needed for this purpose. This requires certain radiation storage. Generally, authors propose different variations of Fabry-Perot cell (see for example [1]), which have sufficiently strong limitations such as a laser beam quality, optic elements stabilization and other. In [2] a new concept of open adiabatic photon trap has been suggested. First successful results on quasi-stationary neutralization of negative ion beams were presented in [3]. This paper contains additional studying process of photoneutralization and more accurate efficiency measurement of hydrogen and deuterium negative ions beams.
Photon storage trap is designed as a system of parallel placed mirrors 25 cm long, consisting of individual cylindrical and spherical mirrors with a dimension of 30mmx50 mm and a radius of curvature of 250 mm. The effectiveness of this approach is mainly determined by the quality of the reflecting surface. It is practically independent from the quality of the injected radiation and does not require high precision alignment of optical elements. In such a system, the photons undergo multiple reflections. Experiments were carried out using an injector with a beam energy 6-12 keV and a current of 1 uA, the laser power up to 2 kW. Neutralization coefficient obtained for negative hydrogen ions is ~90% and ~98% for deuterium.
Based on the obtained results, the concept of a neutralizer for large neutral injection systems was proposed. It contains estimates for the parameters of the required non-resonance adiabatic storage of photons, a laser source, and protection from particle fluxes to mirrors.
References
[1] A. Simonin, L. Christin, H. de Esch, et. al., SIPHORE: Conceptual study of a high efficiency neutral beam injector based on photo-detachment for future fusion reactors . AIP Conf.Proc. 1390 (2011) 494-504.
[2] Popov S.S., Burdakov A.V., Ivanov A.A., Kotelnikov I.A. Photon trap for neutralization of negative ion beams.
Preprint: http://arxiv.org/ftp/arxiv/papers/1504/1504.07511.pdf
[3] M. G. Atlukhanov, A. V. Burdakov, A. A. Ivanov, A. A. Kasatov, A. V. Kolmogorov, S. S. Popov, , M. Yu. Ushkova, and R. V. Vakhrushev. The research of photoneutralization of negative hydrogen and deuterium ion beams in non-resonance photon open trap. AIP Conference Proceedings 1771, 030024 (2016); doi: 10.1063/1.4964180.
